(1) Field of the Invention
The present invention relates in particular to the field of powered aircraft, in particular airplanes and rotorcraft, and more particularly to the field of accessories for fitting to such aircraft. The invention provides an anti-crash seat for a vehicle, and in particular for powered aircraft. The seat includes means for protecting a passenger in the event of a violent impact and/or of a sudden change in the speed of the aircraft, in particular during a crash.
(2) Description of Related Art
Seats for powered aircraft such as airplanes, rotorcraft, and more particularly helicopters or analogous powered aircraft incorporate means for protecting passengers installed on the seats in the event of a crash. The term “passenger” should be understood as designating any person on board the aircraft, whether a pilot or a person being transported. Such protection means are commonly constituted by energy absorber means that are suitable for compensating the stresses to which the seat is subjected when it is subjected to a violent impact and/or to a sudden deceleration, in particular in the event of a crash.
In a common embodiment, the seat associates a frame and a bucket, itself made up of a seat proper with a back extending upwards therefrom. The frame is anchored to the floor of the aircraft via longitudinally extending members and it includes upright legs that are secured to the longitudinally extending members and that together carry the bucket.
According to document EP 0 814 020, an anti-crash seat for a vehicle comprises a bucket for receiving a person and a frame for connecting the bucket to the floor of the vehicle, the bucket being provided with a seat proper and with a back.
The frame is provided with first and second feet, each extended by an upright support leg having a rib. In addition, the seat is provided with one fastener element per upright leg, the fastener elements being supported by the back of the bucket. Each rib is then engaged in a channel in the associated fastener element, with the portion of the rib situated above the fastener element having a cross-section that is smaller than the section of the portion of the rib that is situated below the fastener element.
In the event of the vehicle, e.g. a helicopter, crashing, the downward movement of the vehicle is stopped suddenly and violently when the vehicle makes contact with the ground. Because of its inertia, the bucket with the person sitting on the bucket tends to continue moving downwards, and the fastener elements slide along the ribs which then act as guide means. In addition, the fastener elements plane away the ribs as they move downwards, thereby enabling said rib to act as an energy absorber, specifically absorbing the energy that comes from the kinetic energy of the bucket plus the person sitting on it.
Consequently, the deceleration to which the bucket and said person are subjected is significantly reduced by the ribs of the upright support legs. That first seat thus provides means that act both as guide means and as energy absorber means, with the removal of material from the energy absorber means being found to be highly effective.
Nevertheless, after the crash, the supporting upright legs and the fastener elements need to be replaced, and that gives rise to non-negligible expense.
Document EP 0 078 479 discloses a second anti-crash seat provided with a first structure comprising a frame and a bucket fastened to the frame. Furthermore, the second seat is provided with two pillars suitable for being fastened to a framework of a vehicle.
The frame possesses two sleeves, each sleeve being suitable for sliding on a respective pillar. The pillars then act as guide means.
In order to prevent the sleeves from sliding under normal conditions, i.e. when not in a crash situation, the seat has a plurality of bars fastened via their top ends to cap members arranged at the top ends of the pillars. More precisely, the seat has one cap member per pillar, each cap member being fitted with four bars. Furthermore, each pillar is surrounded by a drawing die itself surrounded by a collar. The bars of a pillar pass through a passage formed in the die of the pillar. It should be observed that the diameter of each bar beneath the die is greater than the diameter of the passage through the die.
Thus, as for the first seat, when the bucket moves down quickly as a result of a crash or a hard landing, the bars are deformed by the die, thereby enabling a large quantity of energy to be absorbed. In contrast, the guide means, namely the pillars, are dissociated from the energy absorber means, namely the bars. After a hard landing, it is only the bars and the dies that need to be changed, thereby limiting cost.
Nevertheless, such replacement requires the seat to be almost completely dismantled. Furthermore, the costs of fabricating the seat remain relatively high because of its close manufacturing tolerances.
According to document FR 2 930 520, an anti-crash seat for a vehicle comprises a bucket and a frame for connecting the bucket to the floor of the vehicle, the bucket being provided with a seat proper and a back for receiving a person, the frame being provided with first and second feet suitable for fastening to the floor on either side of the bucket, said first and second feet being mechanically connected to first and second upright legs supporting the back. In addition, that seat has support means secured to the first and second upright support legs and guide means for guiding the bucket in translation and energy absorber means that are distinct, the guide means and the energy absorber means each co-operating with control means secured to the back of the seat bucket, the guide means co-operating with the control means to guide the movement of the bucket in translation in a predetermined direction during a crash, the energy absorber means co-operating with the control means and with the support means to absorb the kinetic energy of the seat in order to control the deceleration to which the person sitting on the seat is subjected.
Consequently, during a crash, the energy absorber means deforms, with a fraction of the energy absorber means being held stationary by the support means while the control means pull on another fraction of the energy absorber means. The elastic or plastic deformation of the energy absorber means then enables it to absorb energy.
The seat thus serves to protect a sitting person in the event of a vertical crash.
Furthermore, on a rotorcraft, and in particular a helicopter, the seat is heavily stressed in terms of vibration. Under such circumstances, the seat proper is generally covered in a foam lining in order to limit vibratory stress.
Thus, the seat has crash energy absorber means and antivibration means, i.e. the foam. It can be understood that throughout the description the term “energy absorber means” designates means suitable for absorbing the energy that results from a strong acceleration or deceleration during a crash, in particular to protect a person's lumbar region, and the term “antivibration means” designates means serving to avoid transmitting vibration from the vehicle to said person in order to improve comfort.
Although effective, if the antivibration means are stressed little by the weight of the passenger, the crash energy absorber means are activated only after the residual stroke of the vibration absorber means has been used up. In other words, at the moment of a crash, the person moves and stresses the antivibration means, i.e. flattens the foam. The person is thus subjected to an increase in speed before beginning to stress the crash energy absorber means. During a crash, this movement in translation of the person is stopped suddenly. This gives rise to a lumbar force peak when the crash energy absorber means are initially stressed. In compliance with the requirements for certification and in particular the rule known under the name “FAR part 29” that is applicable to rotorcraft, the force peak is acceptable so long as it remains below a specified maximum peak.
Manufacturers thus take that maximum peak into consideration, e.g. when dimensioning the foam.
Document U.S. Pat. No. 3,420,475 describes a seat provided with a piston suitable for sliding in a first cylinder acting as antivibration means, the first cylinder being placed in a second cylinder acting as crash energy absorber means. Although attractive, that solution is also likely to generate a lumbar force peak that needs to be kept within an acceptable limit.
Document FR 2 397 981 proposes a seat fastened to two sliders by a plurality of dampers, each slider being arranged on a rail fastened to a floor. In addition, the connection between a damper and a slider includes antivibration means provided with a block including an element of elastic material associated with a mount. That device can avoid generating lumbar force peaks, but it presents the drawbacks of being relatively bulky and heavy.
Finally, it should be observed that document U.S. Pat. No. 4,003,534 describes a seat provided with means for combating lateral vibration, as opposed to so-called “vertical” vibration directed in a direction that is substantially parallel to the seat back.
The state of the art further includes the following documents: US 2008/015753, U.S. Pat. No. 4,523,730, EP 2 113 457, EP 0 682 191, and DE 10 2008 056661. Document US 2008/015753 provides in particular antivibration means that are fastened on a base, the antivibration means co-operating with means for separating the antivibration means from the base.